CN108119583B

CN108119583B - Ball screw type electromechanical brake

Info

Publication number: CN108119583B
Application number: CN201710301569.5A
Authority: CN
Inventors: 李重熙; 丁钟允; 玄东润
Original assignee: Hyundai Motor Co
Current assignee: Hyundai Motor Co
Priority date: 2016-11-29
Filing date: 2017-05-02
Publication date: 2020-11-17
Anticipated expiration: 2037-05-02
Also published as: US10337575B2; US20180149221A1; DE102017108784B4; KR20180060733A; KR102383332B1; DE102017108784A1; CN108119583A

Abstract

The invention discloses a ball screw type electromechanical brake. The electromechanical brake may include a driving apparatus for an electromechanical brake applying a non-circulating type ball screw, which includes a driving apparatus, i.e., an electromechanical brake having a non-circulating type ball screw, in which pad wear is compensated for by a ball screw, a torsion spring, and a ball holder installed at the other side of the torsion spring, and may automatically compensate for a position movement amount of balls due to pad wear.

Description

Ball screw type electromechanical brake

Technical Field

The present invention relates to electromechanical brakes, and more particularly to electromechanical brakes employing ball screws.

Background

Generally, a brake apparatus for a vehicle is an apparatus that generates a braking force to decelerate or stop an operating vehicle or maintain the vehicle in a stopped state, when the vehicle decelerates, kinetic energy of the vehicle is converted into thermal energy by mechanical friction while braking is performed, and the frictional heat is radiated to the atmosphere.

As a brake apparatus for a vehicle, there are a drum type hydraulic brake, a disc type hydraulic brake, etc., which does not use a drum but obtains a braking force by pressing friction pads against both surfaces of a disc, which rotates together with a wheel.

However, the hydraulic brake has a complicated structure, and since the hydraulic brake requires mechanical elements connected to a brake pedal at a driver seat, hydraulic lines, elements for controlling hydraulic pressure, and the like, an electromechanical brake (EMB) has been developed for simplifying the construction of a brake apparatus.

Unlike a general hydraulic brake, an electromechanical brake denotes a brake in which a braking force is obtained by pressing friction pads by using a mechanical mechanism driven by an electric motor.

A general electromechanical brake has an actuator including an electric motor that rotates back and forth to perform a braking operation (pressing friction pads) and a releasing braking operation (reducing pressure), and is configured to operate using a rotational force of the motor to press the friction pads, which press a disc (causing friction with the disc) while performing the braking operation.

Compared with a hydraulic brake, an electromechanical brake has a simple structure and high response speed and can be controlled more precisely, improving braking safety.

Electromechanical brakes are advantageous because the braking force is controlled, and can be used to implement brake-by-wire (BBW) systems.

As described above, the electromechanical brake generates a braking force from electricity by using a motor and a mechanical transmission, in which case most of the electromechanical brakes use the principle of a screw nut structure and converts a rotational force of the motor into a linear force to press the friction pads.

In the screw nut structure, a ball screw may be used, in which balls are interposed between the nut and the screw, wherein force is transmitted through the balls to reduce frictional resistance.

The ball screw is divided into a circulation type ball screw in which balls circulate and a non-circulation type ball screw in which balls do not circulate. The circulation type ball screw may be applied to a case where the operation section is long and continuous, and the non-circulation type ball screw may be limitedly applied to a case where the operation section is short and discontinuous, even though the non-circulation type ball screw is advantageous in terms of packaging because the outer diameter of the nut may be reduced. Meanwhile, since the amount of movement of the piston in the electromechanical brake is not large, the non-circulating type ball screw may be applied to the electromechanical brake. However, in the electromechanical brake, the ball is configured to move gradually due to pad wear, and thus a technique of restoring the position of the ball is required.

The information disclosed in this background section is intended to enhance an understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.

Disclosure of Invention

Various aspects of the present invention provide an electromechanical brake having a driving apparatus for an electromechanical brake applying a non-circulating type ball screw, and which can automatically compensate for a position moving amount of balls caused by pad wear.

Various aspects of the present invention provide an electromechanical brake comprising: a piston pressing the friction pad; and a driving apparatus providing a force moving the piston, wherein the driving apparatus includes a nut member coupled to the piston and configured to transmit the axial moving force to the piston, a screw coupled to the nut member and rotated to move the nut member in the axial direction, balls interposed between the nut member and the screw and transmitting a rotational force of the screw to the nut member, a ball holder mounted to a second side of the torsion spring and disposed adjacent to a ball at a rearmost end of the balls interposed between the nut member and the screw, and the ball holder configured to contact and press the ball when brake torsion is applied.

In an exemplary embodiment, a head for pressing an inner end of the piston may be formed at a first end of the nut member and a support groove for receiving the ball holder and the torsion spring may be formed at a second end of the nut member.

In another exemplary embodiment, a support end for preventing the ball retainer from moving toward the ball may be formed in the support groove.

In yet another exemplary embodiment, the torsion spring may be disposed in a compressed state on the support end so as to have an initial installation force.

In yet another exemplary embodiment, the ball retainer may be configured to have a clearance with the ball prior to brake pressurization.

In still another exemplary embodiment, the ball retainer may form a gap with the ball even after the braking operation is released.

In yet another exemplary embodiment, at least one retainer groove may be formed in an inner surface of the ball retainer to receive the ball.

In yet another exemplary embodiment, at least one unjoined portion may be formed in the ball retainer, wherein the retainer groove is not formed on the entire inner surface of the ball retainer.

In still another exemplary embodiment, a concave curved shape may be formed at an end of the groove of the holder as the depth of the groove increases, based on the unconnected portion.

In yet another exemplary embodiment, the nut member may have a guide groove in which the plurality of balls are configured to move, and an inner diameter of the holder groove may be equal to an inner diameter of the guide groove.

In yet another exemplary embodiment, at least one protrusion may be formed on the ball retainer so as to prevent the ball from moving backward.

In still another exemplary embodiment, the protrusion may have a curved shape of which a protrusion height decreases leftward and rightward from a center of the protrusion, and the protrusion may have a predetermined area configured to increase from an inner surface of the ball retainer to an outer surface of the ball retainer, wherein a sidewall of the protrusion has a concave curved shape.

According to an exemplary embodiment of the present invention, an electromechanical brake operating in a ball screw type may be implemented, and thus it is possible to improve operation efficiency and durability of a driving apparatus by reducing frictional resistance.

According to the exemplary embodiments of the present invention, since the non-circulation type ball screw may be applied, it is possible to reduce the size and is advantageous in terms of packaging.

It also automatically compensates for ball movement due to pad wear, thus enabling continuous use of the electromechanical brake without the need to separately compensate for pad wear.

Other aspects and exemplary embodiments of the invention are discussed below. It should be understood that the term "vehicle" or "vehicular" or other similar terms as used herein generally includes motor vehicles such as passenger automobiles including Sport Utility Vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft including a variety of boats, ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from non-petroleum sources). As referred to herein, a hybrid vehicle is a vehicle having at least two power sources, such as both gasoline-powered and electric-powered vehicles.

Other features and advantages of the methods and apparatus of the present invention will be more particularly apparent from or elucidated with reference to the drawings described herein, and subsequently, described in conjunction with the accompanying drawings, which serve to explain certain principles of the invention.

Drawings

FIG. 1 is a cross-sectional view of an electromechanical brake according to an exemplary embodiment of the present invention;

fig. 2 is a cross-sectional perspective view showing a main operation device of the electromechanical brake according to the exemplary embodiment of the present invention;

FIG. 3 is a cross-sectional perspective view of the nut of the primary operating device shown in FIG. 2;

fig. 4 is a perspective view showing the ball retainer of the main operation device shown in fig. 2;

fig. 5A, 5B, 5C and 5D are views showing the movement of the screw and the nut, in which fig. 5A shows a state before the balls and the ball retainers are brought into contact with each other, fig. 5B shows a state while brake pressurization is performed, fig. 5C shows a state in which pad abrasion occurs due to continuous brake pressurization, and fig. 5D shows a state after a brake operation is performed;

fig. 6A, 6B, 6C and 6D are views showing movement of the ball with respect to the ball retainer, wherein fig. 6A shows a state before the ball and the ball retainer contact each other, fig. 6B shows a state while brake pressurization is performed, fig. 6C shows a state where pad abrasion occurs due to continuous brake pressurization, and fig. 6D shows a state after a brake operation is performed;

fig. 7 is a view showing a state in which the position of a ball is adjusted by wear of a ball holder compensation pad, wherein a) step in fig. 7 shows a state before the ball and the ball holder are in contact with each other, b) step and c) step in fig. 7 show a state while brake pressurization is performed, d) step in fig. 7 shows a state while a spring is extended when the brake is released, e) step in fig. 7 shows a state while the brake is released to compensate for the wear, and f) step in fig. 7 shows a state in which the brake is completely released and the ball is restored to its original position;

FIG. 8A is a graph showing ball nut friction and spring force versus screw rotation angle prior to a braking operation;

fig. 8B is a graph showing a change in the frictional force and a change in the spring force of the ball in a state where the friction pad is worn;

fig. 9 is a cross-sectional perspective view showing a main operation device of an electromechanical brake according to another exemplary embodiment of the present invention; and is

Fig. 10 is a perspective view showing the ball retainer of the main operation device shown in fig. 9.

It is to be understood that the appended drawings are not to scale, showing a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the invention disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, will be determined in part by the particular application and environment of use contemplated.

In the figures, reference numerals refer to equivalent parts of the invention throughout the several views of the drawings.

Detailed Description

Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with the exemplary embodiments, it will be understood that this description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only these exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

The electromechanical brake according to the exemplary embodiment of the present invention is characterized in that the non-circulating type ball screw is applied to a driving device that transmits a driving force of a motor to apply a clamping force of a caliper housing when the motor is configured to operate to generate a braking force. The electromechanical brake according to an exemplary embodiment of the present invention is further characterized in that, when the non-circulating type ball screw is applied to a driving apparatus, the ball retainer is provided at the first end of the nut so as to compensate for the position displacement of the ball due to pad wear. The ball retainer is provided together with an elastic member disposed in a pad wear direction, and is configured to compensate for pad wear by using a return force of the elastic member.

A ball screw type electromechanical brake according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a cross-sectional view of an electromechanical brake according to an exemplary embodiment of the present invention, and fig. 2 is a cross-sectional perspective view showing a main operation device of the electromechanical brake according to an exemplary embodiment of the present invention. Further, fig. 3 is a cross-sectional perspective view of a nut member of the main operation device shown in fig. 2, and fig. 4 is a view showing a ball retainer of the main operation device shown in fig. 2.

As shown in fig. 1, an electromechanical brake 100 according to an exemplary embodiment of the present invention includes a bracket fixedly disposed on a vehicle body, and a caliper housing 120 coupled to the bracket so as to be movable forward and backward, and disposed to surround a first side of a disc 1 disposed in a wheel.

In the bracket, a pair of friction pads (brake pads) 121 and 122 are provided to be movable back and forth, the

friction pads

121 and 122 pressing both surfaces of the disk 1 rotating together with the wheel.

A pair of

friction pads

121 and 122 are provided to be spaced apart from each other, and the disk 1 is disposed between the pair of

friction pads

121 and 122. Therefore, when the piston 124 to be described later is configured to move forward, the friction pad 121 is configured to move toward the disk 1 to cause friction with the disk and press the disk, performing a braking operation.

The caliper housing 120 is slidably disposed on the bracket and has a cylinder 123 with a piston 124 disposed in the cylinder 123.

That is, a hollow cylinder 123 is formed at the first side of the caliper housing 120, and a piston 124 is provided in the cylinder 123 so as to be movable forward and backward.

The piston 124 is configured to move forward to move one friction pad 121 of the pair of

friction pads

121 and 122 forward toward the disk 1, wherein the friction pad 121 is caused to rub against the disk 1.

A finger portion 126 is formed at the second side of the caliper housing 120, the finger portion 126 being configured to move the second friction pad 122 forward toward the disc 1, wherein the second friction pad 122 is caused to rub against the disc 1.

Accordingly, the piston 124 is configured to move forward toward the friction pad 121 and the disc 1 by a force transmitted for braking, thus pressing the first friction pad 121 against the disc 1, and the caliper housing 120 is configured to move in a direction opposite to the moving direction of the piston 124 by a reaction force applied between the piston 124 and the first friction pad 121, wherein the finger portion 126 of the caliper housing 120 presses the second friction pad 122 against the disc 1.

Thus, the two

friction pads

121 and 122 press both surfaces of the disc 1 at the same time.

In this case, a braking operation is performed by a frictional force generated between the two

friction pads

121 and 122 and the disc 1, and the frictional force generates a braking force to restrict the wheel so that the wheel cannot rotate.

Here, the force of the piston 124 and the finger portion 126 of the caliper housing 120 pressing the

friction pads

121 and 122 against both surfaces of the disc 1 may be referred to as a clamping force of the caliper housing 120, and a reaction force generated when the clamping force is applied from the friction pad 121 to the piston 124 while a braking operation is performed (i.e., pressing the friction pads).

Meanwhile, the electromechanical brake 100 according to the exemplary embodiment of the present invention includes a driving apparatus for operating the piston 124. The driving apparatus includes a nut member 131 and a screw 132, the nut member 131 being coupled to the piston 124 provided in the cylinder 123 of the caliper housing 120 and configured to move back and forth in an axial direction (configured to move linearly back and forth) to allow the piston 124 to move back and forth, the screw 132 being coupled to the nut member 131 and rotated to allow the nut member 131 to move back and forth (move linearly back and forth). Further, in the present exemplary embodiment, the driving apparatus is understood to further include an electric motor 140 that provides a rotational force to generate a braking force, and a gear assembly 141 that is disposed between a rotational shaft of the electric motor 140 and the screw 132 and transmits the rotational force of the electric motor 140 to the screw 132.

The electric motor 140 of the driving apparatus is a driving source generating a driving force, i.e., a rotational force for performing a braking operation (pressing) and releasing the braking operation (reducing pressure), and rotates forward while pressing the friction pads and rotates backward while reducing the pressure on the friction pads, wherein the electric motor 140 generates a forward rotational force and a backward rotational force and provides the forward rotational force and the backward rotational force to the screw 132 through the gear assembly 141.

The operation of the electric motor 140 is configured to be controlled by a controller, and the controller is configured to control the forward operation and the backward operation of the motor 140.

The screw 132 is coupled to a shaft of an output gear 142 of a gear assembly 141, and the gear assembly 141 is a constituent element that reduces the rotational speed of the motor 140, amplifies the rotational force of the motor 140, and thus transmits the rotational force to the screw 132, and the gear assembly 141 may be configured in the form of a gear train including a gear combination.

The electric motor and gear assembly that has been applied to the known electromechanical brake 100 is configured to be applied in the form of an electric motor 140 and a gear assembly 141.

Meanwhile, in the present exemplary embodiment, the driving apparatus is a ball screw type that converts a rotational motion of a screw into a translational motion of a piston by balls 134 interposed between a bolt 132 and a nut member 131.

First, the piston 124 of the caliper housing 120 has a hollow portion 125 therein extending and elongated in an axial direction (i.e., the same axial direction as the forward and backward moving direction of the piston), and the nut member 131 is disposed and coupled in the hollow portion 125 of the piston 124.

As shown in fig. 3, the nut member 131 has an elongated cylindrical shape and has a head 131d formed at an end of the nut member 131 and configured to contact the inner end 124a of the hollow portion 125 of the piston 124 to press the inner end 124a of the hollow portion 125.

A spiral guide groove 131a is formed in the inner surface of the nut member 131 along the circumference of the inner surface. The guide groove 131a is configured to guide movement of the balls between the screw and the nut member 131, and the guide groove 131a has a length so that the movement of the balls is controlled by the length in consideration of the number of balls contained in the ball screw.

The nut member 131 is assembled around the outer circumference of the screw, and the nut member 131 is configured to move along the outer surface of the screw by a plurality of balls interposed between the outer surface of the screw and the inner surface of the nut member 131. That is, when the screw is rotated according to the operation of the electric motor, the nut member and the piston 124 connected to the nut member are configured to be moved by the balls in a linear manner.

For this reason, guide grooves corresponding to the guide grooves 131a of the nut member 131 are also formed in the screw, and a plurality of balls are disposed between the guide grooves.

Meanwhile, in the present exemplary embodiment, a cylindrical support groove 131b is formed at a second end portion of the nut member 131 (i.e., at an end portion opposite to the first end portion where the head portion 131d is formed), the cylindrical support groove 131b accommodating the ball retainer 133 and supporting the ball retainer 133. As shown in fig. 2, the ball holder 133 and the spring member 135 for elastically supporting the ball holder 133 are inserted into the support groove 131b, and a support end 131c for restraining the ball holder 133 is formed at a first end of the support groove 131 b.

As shown in fig. 2 and 3, the ball retainer 133 has a ring shape inserted along the outer circumference of the screw. The ball holder 133 is elastically supported by a spring 135, a first end of the spring member 135 is fixed to the nut member, and a second end of the spring member 135 is fixed to the ball holder 133. In the present exemplary embodiment, the spring member 135 is a torsion spring, and the spring member 135 is configured to be twisted and compressed when an external force is applied to the spring 135.

As shown in fig. 2, the ball retainer 133 is basically mounted on the nut member by a spring 135, and thus the ball retainer and the nut member move together. However, in case the ball retainer 133 and the nut move relative to each other, the spring member 135 compresses and provides a return force relative to the balls. Thus, the spring member 135 is a constituent element that restores the ball position when the braking operation is released.

A holder groove 133a is formed in the ball holder 133 to support the ball and transfer force applied by the ball. The holder groove 133a is formed in the side surface of the holder facing the ball, and the holder groove 133a is not formed on the entire inner surface of the holder but has at least one unconnected portion 133 c. The unconnected portion 133c denotes an inner surface of the retainer where no groove is formed, and the unconnected portion 133c is configured to guide the ball (where the ball may be seated in the retainer groove 133 a) and transmit a force of the ball pressing the ball retainer 133 to the spring 135. Therefore, the unconnected portion 133c of the holder groove is formed in the shape shown in fig. 4, and the shape of the end of the holder groove 133a has a concave curved shape as the depth of the groove increases based on the unconnected portion 133 c. Therefore, the balls can roll and move on the surface of the holder groove by the concave curved shape of the end of the holder groove 133 a. For example, when the balls press the ball holder 133, the spring member 135 is compressed, and the ball holder 133 is configured to move backward (in the rightward direction of fig. 2).

Fig. 4 shows that two holder grooves are provided to include a second unconnected portion at a portion opposite to the one unconnected portion 133c shown previously, but the number of holder grooves is not limited thereto, and it is also conceivable that a single groove or at least two grooves may be provided.

Meanwhile, it is necessary to initially set the position of the unjoined portion 133c in the retainer groove to correspond to the position of the ball on the rearmost side of the ball screw. The reason for this is to allow the balls to compress the spring member 135 without delay while moving to a precise position in the holder groove 133 a.

The holder groove is configured to accommodate the balls of the ball screw at a predetermined time, and the inner diameter of the holder groove is set to correspond to the inner diameter of the guide groove 131a of the nut member.

As described below, in the initial state, the inserted ball is set to maintain a non-contact state with the ball holder 133. Accordingly, in a non-contact state between the ball retainer 133 and the balls at the rearmost end of the ball screw, the nut translation motion is performed by the rotation of the screw, and thus the nut member 131 can be configured to move while the balls are maintained in the non-contact state, improving the efficiency of the driving apparatus. Further, as shown in fig. 2 and 3, a support end 131c is formed at a first end of the support groove 131b, and the spring member 135 may be compressed and supported by the support end 131c to have an initial installation force (which is required to allow the spring to be in an initial compressed state). When the initial installation force is applied to the spring member 135 as described above, the non-contact state between the balls and the ball holder 133 can be maintained by the initial installation force even if the braking operation is released.

Fig. 5A, 5B, 5C, and 5D show the movement of the screw and the nut, and fig. 6A, 6B, 6C, and 6D show the movement of the ball with respect to the ball retainer 133 in the case corresponding to the cases of fig. 5A, 5B, 5C, and 5D.

In the present exemplary embodiment, since the initial setting is made so as to avoid the balls and the ball retainer 133 from contacting each other, the balls and the ball retainer 133 do not contact each other at the time when the ball screw starts to operate, as shown in fig. 6A. In this case, as shown in fig. 5A, the disk and the friction pad are in a non-contact state, and the nut member 131 starts moving forward.

Fig. 5B is a diagram showing a state while brake pressurization is performed, and during brake pressurization, the disc and the friction pad are in contact with each other, and a braking operation is performed. As shown in fig. 6B, during brake pressurization, the balls are configured to move backward by the brake reaction force and come into contact with the ball retainer 133.

Fig. 5C shows a state where pad abrasion occurs due to continuous brake pressurization, and in this case, as shown in fig. 5C, the ball completely moves to the holder groove 133a of the ball holder 133 while moving backward, and compresses the spring while pressing the unconnected portion 133C of the ball holder 133.

Thereafter, when the braking operation is released, the nut member 131 and the piston 124 are configured to be moved rearward by the rotation of the screw. Fig. 5D is a diagram showing a state after a braking operation is performed, and in the present exemplary embodiment, after the braking operation is performed, the piston 124 and the nut are moved forward by the abrasion amount of the friction pad by the return force of the spring member 135.

The operating mechanism of the ball screw according to the present exemplary embodiment is described in more detail with reference to fig. 7.

First, step a) in fig. 7 shows a state before the balls and the ball holder 133 are in contact with each other, and shows the same state as fig. 5A and 6A. The balls do not contact each other, and there is no sliding resistance between the balls.

Thereafter, when the friction pad and the disc are brought into contact with each other and brake pressurization is performed, a frictional force is generated in the relationship between the ball and the nut and the screw, and the ball and the nut are configured to move relative to each other, as shown in step b) of fig. 7. Thereafter, as shown in step c) of fig. 7, the gap between the ball and the ball holder 133 disappears and the spring member 135 starts to be compressed.

Meanwhile, when the braking operation is released, the frictional force of the ball is greater than the returning force of the spring at the initial time, so that the spring is extended by the distance the ball moves when the ball moves, as shown in the step d) of fig. 7.

In contrast, as shown in fig. 8B, when the friction pad is worn, the frictional force between the ball and the nut is reduced, and the braking operation is released due to the reduction of the frictional force, so that the frictional force of the ball is smaller than the return force of the spring. This state is shown in step e) of fig. 7, since the restoring force of the spring is greater than the frictional force of the balls, wear is compensated as the balls are pushed by the ball holder 133 while the spring is extended. Therefore, in the present exemplary embodiment, the abrasion amount of the friction pad may be compensated for by the restoring force of the spring member 135 installed in the ball retainer 133.

In this regard, fig. 8A is a graph showing the ball nut frictional force and the force of the spring member with respect to the screw rotation angle before the braking operation is performed, and fig. 8B is a graph showing the change in the frictional force of the balls and the change in the force of the spring member in a state where the friction pads are worn. Fig. 8A and 8B show embodiments of setting the initial installation force for the spring member 135, in which the nut member 131 may be additionally configured to move at a time point at which the supporting end 131c of the nut member 131 starts to restrict the movement of the ball retainer 133 (i.e., a time point before the complete force balance is achieved by the initial installation force, i.e., a time point at which the line D and the line B cross in fig. 8B). Therefore, when the braking operation is released, the balls are configured to move even after the ball holder 133 is stopped, and thus the gap between the balls and the ball holder 133 can be maintained.

Meanwhile, fig. 9 is a cross-sectional perspective view illustrating a main operating device of an electromechanical brake according to another exemplary embodiment of the present invention, and fig. 10 is a perspective view illustrating a ball holder 233 of the main operating device illustrated in fig. 9.

The present exemplary embodiment is the same as the previous exemplary embodiment except that the ball retainer 233 has the structure shown in fig. 10. Thus, as with the previous exemplary embodiment, the present exemplary embodiment includes a ball screw structure including a nut member 231, a screw 232, and balls 234. According to the present exemplary embodiment, the ball retainer 233 has at least one protrusion 233a, and a sidewall of the protrusion 233a has a curved surface instead of a structure having a groove.

That is, as shown in fig. 9 and 10, the protruding portion 233a of the ball retainer 233 according to the present exemplary embodiment has a structure that protrudes toward the balls 234 accommodated between the nut member 231 and the screw 232 so as to be in contact with the balls. The side wall of the side of the protrusion 233a has a curved surface to move and support the ball, and when the ball applies force to the ball holder 233, the protrusion 233a is configured to transmit the force and compress the spring member 235 in the form of a torsion spring. Therefore, the protruding portion 233a has a curved shape whose protruding height decreases leftward and rightward from the center. Further, the protrusion 233a may be configured to have a predetermined area configured to increase from the center of the ball holder 233 having a ring shape to the outside (i.e., from the inner surface of the protrusion 233a to the outer surface of the protrusion 233 a), so the protrusion 233a may receive the ball and may effectively transmit the force from the ball to the spring member without having a gap with the ball. A single protrusion may be provided, or a pair of

protrusions

233a and 233b may be provided as shown in fig. 10.

Since the operating mechanisms of the ball retainers and the spring members are substantially the same as those described above, descriptions thereof will be omitted.

For convenience in explanation and accurate definition in the appended claims, the terms "upper", "lower", "inner", "outer", "high", "low", "upper", "lower", "upward", "downward", "front", "rear", "back", "inside", "outside", "inward", "outward", "inside", "outside", "inner", "outer", "forward" and "rearward" are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable others skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

1. An electromechanical brake device comprising:

a piston configured to press the friction pad; and

a drive apparatus configured to provide a force to move the piston,

wherein the drive apparatus includes a nut member, a screw, a plurality of balls, a torsion spring, and a ball retainer, the nut member is coupled to the piston and configured to transmit an axial movement force to the piston, the screw is coupled to the nut member and rotated to move the nut member in an axial direction, the balls are configured to be interposed between the nut member and the screw rod and to transmit a rotational force of the screw rod to the nut member, a first side of the torsion spring is mounted to the nut member, the ball retainer is mounted to a second side of the torsion spring and disposed adjacent to a ball at a rearmost end of balls interposed between the nut member and the screw, and the ball retainer is configured to contact the ball and press the torsion spring when brake pressurization is performed.

2. The electromechanical brake device according to claim 1, wherein a head for pressing an inner end portion of the piston is formed at a first end portion of the nut member, and a support groove for accommodating the ball retainer and the torsion spring is formed at a second end portion of the nut member.

3. An electromechanical brake device according to claim 2, wherein a support end is formed in the support recess for preventing the ball retainer from moving towards the ball.

4. An electro-mechanical brake arrangement according to claim 3, wherein said torsion spring is arranged to be constrained in compression on said support end so as to have an initial installation force.

5. An electromechanical brake device according to claim 1, wherein the ball retainer is arranged to have clearance with the balls prior to brake pressurisation.

6. An electromechanical braking apparatus according to claim 5, wherein the ball retainer is still in clearance with the balls even after the braking operation is released.

7. An electromechanical brake device according to claim 1, wherein at least one retainer recess is formed in an inner surface of the ball retainer to accommodate a plurality of balls.

8. The electromechanical brake device according to claim 7, wherein at least one unconnected portion is formed in the ball retainer such that the retainer groove is not formed over the entire inner surface of the ball retainer.

9. The electromechanical brake device according to claim 8, wherein a concave curved shape is formed at an end of the holder groove as the depth of the groove increases based on the unconnected portion.

10. An electro-mechanical brake device according to claim 7, wherein said nut member has a guide groove in which a plurality of balls are configured to move, and an inner diameter of said retainer groove is equal to an inner diameter of said guide groove.

11. The electromechanical brake device according to claim 1, wherein at least one protrusion is formed on the ball retainer so as to prevent the plurality of balls from moving backward.

12. The electromechanical brake device according to claim 11, wherein the at least one protruding portion has a curved shape whose protruding height decreases leftward and rightward from a center of the protruding portion, and a side wall of the protruding portion has a concave curved shape.